1. Field of the Invention
The present invention relates to a disk storage apparatus having a load/unload mechanism for loading and unloading a recording/reproducing head such as a magnetic head onto or from a disk surface which is a recording medium by an actuator. The invention also relates to a disk storage apparatus for positioning a head on a target track of a disk with high precision by an actuator.
2. Description of the Related Art
In a magnetic disk storage apparatus, with a tendency of downsizing and high storage density, the requirement of high precision positioning of a head with respect to a target track becomes more strict. Further, since it is necessary to flatten a disk surface for increasing the recording density, there is a method for retreating a head slider outward of a disk when the head is not actuated.
In a disk storage apparatus having the head load/unload mechanism, a ramp block as a retreating member is disposed outside the disk. When the apparatus is stopped, a head arm is turned to place the head slider on the ramp block, thereby unloading the head. When the actuation of the apparatus is started, the head arm is turned, the head slider is loaded on the disk from the ramp block.
If the loading speed is too fast, the head slider crashes against the disk, and the disk and the head are damaged In or to smoothly load the head on the disk, it is necessary to stably control speed even on the ramp block.
A voice coil motor (VCM) is used as an actuator which drives the head. Induction voltage generated on both ends of the VCM coil when the VCM is turned is detected by a bridge circuit, and feedback speed control is carried out while using the obtained detection voltage as a speed signal.
On the other hand, in order to quicken the positioning operation of the head with respect to the target track and to secure required positioning precision, it is generally believed that control frequency of positioning control is set higher. However, since a positioning control system becomes unstable due to natural mechanical oscillation of the head actuator, there is a limit for increasing the control frequency of the positioning control. Thereupon, the positioning precision is enhanced by reducing external fore acting on the actuator.
Conventionally, a head position signal obtained from servo information on the disk and a driving signal of the actuator are inputted to estimate the external force, thereby carrying out the feedback control to compensate the external force.
However, although the bridge circuit is simple in circuit structure, the bridge circuit is susceptible to variation in load disturbance caused by friction or the like on the ramp block.
If the variation in load disturbance by the sliding friction between the head slider and the ramp block is great, speed of the head slider is largely varied. Therefore, even if the feedback control is carried out for the head slider moving speed, the variation in head loading speed is great, and possibility of crash of the slider against the disk still remains.
Further, with the recent tendencies of high density of track and downsizing of the actuator, the external force acting on the actuator affects the control system more seriously, and the conventional technique can not sufficiently overcome the problem.